In the ink jet printing art, water soluble dyes are desirable for runnability. However, waterfast inks are highly desirable for producing permanent images. Waterfast non-black inks are highly desirable in ink-jet printing to produce water-resistant prints. Decreasing the solubility of the dye increases the waterfastness, and vice versa. Achieving improvement in waterfastness of ink jet inks remains a top priority. A waterfast ink is highly desired for publishing and documentation, including in the lottery industry, to prevent alteration of information on such documents.
One means for improving waterfastness is to use polymers and resins in inks to enhance adhesion of the dye to substrates. However, presence of resins in inks adversely affects machine runnability due to formation of deposits on orifice plates and charge plate buildup.
In commonly assigned U.S. Pat. No. 5,425,805, totally incorporated herein by reference, a waterfast ink comprising a liquid vehicle, a dye, EPI and NMP is disclosed. The use of ethoxylated polyethylene imine (EPI) and the like in the ink showed significant improvement in waterfastness from a range of 40-60% to a range of 70-95%, depending on the substrate and the dye in the ink. Unfortunately, non-black color dyes achieve only a modest improvement in water resistance with EPI, partially as a result of their extreme solubility. Therefore, it is a challenge in the ink jet printing industry to achieve waterfastness in an aqueous, non-black dye-based ink.
It is seen then that there is a need for improved waterfast color ink for use in ink jet recording equipment.